Let me clarify on some of the speculations regarding the differences in the various perceived differences between the GBE, Shuttles and ShuttleMax's to keep this thread from becoming one of constant second-guessing.
All of these amps were designed and voiced by the same folks. Without pigeon-holing any particular model, the criteria considered things like the size and tuning of the specific cabinet class, style of music and expected SPL, type of player and (to a small degree) their skill and experience level that the class of amp is likely to be used with. All of these amps are switchable between 115/230/240V, making them more attractive to the international touring guys.
For example, the Shuttle 3.0 is unlikely to be desireable to a heavy metal or thrash player because it does not have enough power to be an even remotely reasonable choice but it is definately popular amongst players of Jazz, rock, causals, theatre, praise/worship, and harder styles with good PA support. Also, the 3.0 is popular amongst folks who consider size and weight of the entire rig (including speakers) of prime importance, so to accomodate this the highpass filter is set slightly higher then our other models, which improves the performance of both the amp and the typical sub-compact speakers (by any manufacturer) way down low. Note that the pre-eq DI out on all of our amps is pre HPF, so the signal you send to the board is full bandwidth (all good PA's HPF the subs anyway, so it's not something we need to address and to double up on HPF's would compromise performance).
The Shuttle 6.0 is a more mainstream amp, still probably not the ideal hard-core/metal/thrash amp due to the limited power unless good PA support is available, but will drive larger cabinets with ease. It's voicing includes a HPF with a slightly lower turnover frequency and when combined with the remaining filter and preamp voicing, is more solid into compact and larger cabinets. The LF extend frequency, slope, Q and symmetry is also voiced to improve overall performance into the larger cabinets. The tube voicing also contributes to the perceived warmness, though it's been kept somewhat subtle to be used as a tool rather than jumping out screaming TUBE OVERDRIVE. The Pre-eq DI out is before the HPF's, so into a real PA, there's zero compromise regarding LF bandwidth. This is a popular amp amongst our touring users who must rely on fly dates, it's a simple, straight ahead, compact, lightweight amp with features that a more pro player is likely to need.
The Shuttle 9.0 is very similar to the 6.0, but again has a very slightly lower HPF frequency because we have additional headroom to work with and it's unlikely that this amp would be used (at high volumes or extended low end) with sub-compact cabinets, so we have more margin to work with. The 9.0 pairs nicely with cabinets from the compact (like Neo-X 212) on up, but I caution against expecting such performance with sub-compact speakers like the STL series (or those by other manufacturers) since the amp has too much power and runs the risk of overdriving models without adequate power handling and LF excursion limiting tuning. The 9.0 would be an amp to consider for all styles provided it's paired up to a cabinet that's also suitable.
The ShuttleMax's are very similar to the Shuttle's, there is a slight difference in the voicing because of the added gain (switched) in the front end, the variable tone shaping & voicing filters, additional eq, and slightly different signal path topology. This is why they sound a little different than the Shuttles, and with the Max 12.0 used with 2 x 4 ohm speakers, of course there will be significant additional headroom which does help an amp open up when driven hard. The voicing is probably closest to the 9.0 but must be taken in context with the additional feature set. The Max 12.0 is another amp suitable for all styles when paired with an appropriate cabinet choice. The Max 12 also contains a back-up power supply that will run the entire preamp and second power amp in the unlikely event of a module failure. I do not know of this feature being used at this point, but it's nice to know it's there if you need it.
The GBE 750 & 1200 uses similar but at the same time different signal path topology, clearly these amps are not for a player looking for sub-compact or lightweight so the voicing assumes they will be used with compact or larger cabinets and high volume and low frequency extension are expected. The input voicing is a little different, the slopes and response of the HPF and the interaction with the voicing filters consider the likely player and cabinet type (certaily a better choice for hard core, thrash and heavier metal) to gove an overall different flavor within our typical voicing. The tube channel has a little more gain than the Shuttle 6/9 but less than the Max 12. The 750/1200 will both drive 2 ohm loads directly, the Max will drive a 2 ohm load comprised of 2 x 4 ohm cabinets, each driven by it's own amp module.
All in all, the differences in voicing and LF response between the Shuttle 6/9 and Max 6/12 is really very, very small. Some is due to a perception because there is additional power available which allows for more headroom when playing harder. IIRC, the difference is between 5 and 7Hz, there will be maybe as much variation in speaker response & tuning given the tolerances of the average drivers in a production sampling. Another thing to consider when evaluating perceived warmth is the contribution of the tube, and the variability that each tube brings to the table. While we have tried to minimze the variability between tube samples in the design, we have not eliminated this, so easc tube will sound slightly different.
So, for the techies here I hope this helps, and for you other guys I hope it didn't bore you to death.
